This invention relates to bearing arrangements generally known as of the tilting pad type, wherein a ring of individual bearing pads are arrayed about a rotating article, such as a radially facing shaft journal or an axially facing thrust collar, each pad having an obverse face, against which the article bears and across which it moves, and reverse face, which is supported with respect to a pad carrier such that the pad can undergo a limited degree of tilting at least in the direction of article motion.
The invention relates to both journal and thrust bearing forms but is particularly suited to journal bearings.
It is known from GB-A-1397551 and GB-A-2268549 to have journal bearings wherein essentially cylindrically curved bearing pads are supported against a cylindrical carrier formed by the bearing housing and, from the latter, to have the reverse face of the pad convexly curved in a transverse direction and be seated in a matching concave recess in the housing, permitting the pad to align with respect to the housing to accommodate misalignment between shaft and housing, but to retain its ability to rock with respect to the housing. Such arrangements require the relationship between obverse and reverse faces of each pad and the housing to be maintained for the whole of each pad face and for all pads, including replacements.
It is known from U.S. Pat. Nos. 4,714,357 and U.S. Pat. No. 3,022,123 to have, instead of a shaped reverse pad face, a separately attached pivot member exhibiting a barrel-shaped surface which permits both tilting in the direction of shaft surface motion and orthogonally thereto for alignment.
It is furthermore known, for example from GB-A-2180888, to have bearing pads for journal and thrust bearings supported on spherical surfaces which are unrestricted in direction of tilt, such spherical surfaces offering a point contact between the relatively moving pads and carrier.
Such pad tilt arrangements all function by a xe2x80x9crollingxe2x80x9d of the pad as it tilts, which requires that the pivot arrangement involves a line or point contact through which all bearing loading is transmitted to the pad carrier or housing; such concentration of forces may place constraints on materials employed for the bearing pads and/or pad dimensions to withstand such forces without distortion.
It is also known, for example from GB-B-2292192 and CH-B-558481 to mitigate problems associated with line and point contact by having mating convex and concave surfaces of spherical form whereby the load is transferred over the area of contact between the mating surfaces, rather than a point or line, but at the expense of increased friction in the tilting process. Such spherically curved mating surfaces tend to be of limited extent, both as a compromise between increasing friction and maximising load spreading and to be economially viable.
It will be appreciated that such pivot means which effect contact over an area of co-operating surfaces effect tilting of the bearing pad by rotating it about a primary pivot axis which is fixed with respect to the carrier, such primary pivot axis extending in a direction which is mutually orthogonal to the direction of motion of the article surface across the bearing pad and the direction in which load is transferred thereby into the carrier.
Tilting pad journal bearings are known, for example from WO 96/13672, which are limited to effecting pivoting, in place of tilting, about the primary tilt axis alone.
As well as the variants above, thrust bearings are likewise known in which the reverse face of each thrust pad is supported clear of a carrier by way of a protuberance on either the pad face or carrier, either a spherically curved protuberance giving a point contact as a simple radially-extending fulcrum ridges giving a line contact.
It is an object of the present invention to provide a tilting pad bearing arrangement of the type wherein each pad is supported on pivot means whose surfaces define an area of contact and able to tilt by rotation about more than a primary pivot axis by relative sliding motion between the surfaces, which mitigates the at least some of the constraints on, and complexity and cost of, known arrangements.
According to the present invention a tilting pad bearing arrangement, for supporting an article movable relative thereto in rotation about a rotation axis, comprises a plurality of bearing pads and a load bearing carrier of the pads, each of the pads having an obverse article-supporting face extending in the direction of article motion and a reverse supported face adapted to transfer load to the carrier in a loading direction perpendicular to the motion direction, and associated with each pad, pivot means operable to support the pad separated from the carrier and permit the pad to tilt about a primary tilt axis perpendicular to the motion and loading directions, said pivot means comprising a pad recess formed in the reverse face of the pad, a carrier recess formed in the face of the carrier, and linking means extending between said pad recess and carrier recess, one of the recesses having a cylindrically concave surface centred on the primary tilt axis, the other recess having a cylindrically concave surface centred on a secondary tilt axis perpendicular to the primary tilt axis, and the linking means having defined on each of opposite sides thereof associated with respective recesses a surface of cylindrically convex curvature conforming to the curvature of the associated recess to make sliding contact therewith over the common area of said convex and concave surfaces.
The dimension of each of said convex opposite sides of the linking means in the direction of the cylindrical axis thereof may be substantially equal to the other. Furthermore, the dimensions of each said convex sides of the linking means in the direction of the cylindrical axis thereof may be substantially equal to the dimension of the opposite convex side in a direction perpendicular to the direction of the cylindrical axis of said opposite side.
Preferably at least one of the pad recess and carrier recess comprises a minor sector of the cylinder of which it is part.
The linking means may comprise a unitary body or a stack of linking members, the opposite sides of the linking means being defined by a pair of outer linking members each having a wall of cylindrically convex curvature. There may be provided between the outer linking members intermediate linking means operable to define the separation between said convex surfaces.
In such linking means formed by a stack of linking members there may be provided tie means operable to impede relative movement between the outer linking members at least in a direction in the plane parallel to, or containing, both first and second cylindrical axis.
The tie means may comprise at least one projection and/or recess at the inward facing surface of each outer linking member and a co-operating at least one recess and/or projection in the inward facing surface of the other outer linking member or of the intermediate linking means.
Furthermore, the tie means may be operable to impede separation of the outer linking members with respect to each other.
At least one of said pad and carrier recesses may include boundary means to limit motion of the linking member therealong in at least one direction.